01 Hydrogen Bonds and Properties of Water

Polar Molecule

A molecule with an uneven distribution of charge, like water (H₂O), where oxygen is partly negative and hydrogen is partly positive.

Electronegative

The ability of an atom to attract electrons in a covalent bond; oxygen is electronegative in water.

Hydrogen Bond

A weak bond between the partly positive hydrogen of one molecule and a partly negative atom (like oxygen or nitrogen) of another molecule.

Hydration Shell

The sphere of water molecules around a dissolved ion.

Hydrophobic

"Water-hating"; refers to substances that do not dissolve in water (e.g., oil).

Hydrophilic

"Water-loving"; refers to substances that dissolve in water (e.g., sugar).

Evaporation

The change of a substance from a liquid to a gas.

Heat of Vaporization

The amount of heat required to convert 1 gram of a substance from liquid to gas.

Specific Heat

The amount of heat needed to raise the temperature of 1 gram of a substance by 1 degree Celsius.

Cohesion

The attraction between molecules of the same substance (e.g., water molecules sticking to each other).

Adhesion

The attraction between molecules of different substances (e.g., water molecules sticking to other polar molecules).

Surface Tension

A measure of how difficult it is to stretch or break the surface of a liquid, due to the cohesive forces of water molecules.